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LF: Advice to beginners

To: [email protected]
Subject: LF: Advice to beginners
From: "Mike Dennison" <[email protected]>
Date: Tue, 5 Jun 2001 11:13:18 +0100
In-reply-to: <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
I believe that a simple low power transmitter for 136 kHz would
make an excellent club project, with the very real prospect of
not just making LF QSOs across town - but with other countries
too! Regards to all,
Steve GW4ALG
Whilst it is a great idea to interest clubs in such a project, beware of using low
power into a non-optimised antenna. If I had been restricted to 5W in my
early days I would have given up long ago, and I am sure that Steve would
have done so, too. I could certainly use QRP now as my antenna is so much
better. Any newcomers expecting to do well with 5W =must= be given proper
advice on antennas.

For instance:

Insulate very well indeed.
Keep well away from absorbing things like trees.
Optimise tuning and matching.
Spend some time on earthing.
Antenna current multiplied by =effective= height is the thing to improve.

Be realistic: If you have a 40m dipole, 8m above ground and strapped as a Marconi, over poor soil, you are wasting your time with 5W. Good results will can be had with several hundred watts - easily and cheaply obtainable with a BK Electronics amp.
Also (those who have been on this reflector for years will remember my old
sermon) it is vital to optimise the receiver as you won't work anyone you can't
hear.
This involves:

Good gain distribution.
Keep receive antennas away from local noise sources.
Trace any permanent noise and fix it (for instance, LF radiation from my big TV was cured by adding a few pF in series with each leg of the antenna coax close to the set). Be aware of possible intermod (for instance check 138kHz for a pulsed tone caused by a mix in your receiver between 60kHz Rugby and 198kHz BBC) and fix it.
Perhaps use a directional antenna or noise cancellation.
Enough gain to be able to hear right down into the noise (an IC706 will hear signals but needs a pre-amp to be effective).
Does anyone else have tips for beginners?


Mike, G3XDV (IO91VT)
http://www.lf.thersgb.net



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